Conservation laws in spontaneous and measurement-like individual processes

A critical examination of the main features of quantum and classical mechan ics allowed the authors to formulate a criterion to decide whether conserva tion laws are valid or not in measurement-like individual processes. Postul ates of quantum mechanics regarding measurements were applied to certain pr ocesses occurring in an isolated system consisting of a particle and an ene rgy-measuring device. The analysis of the results suggested that the energy is not conserved in those individual processes. To amend this, the authors assumed that the energy measuring device changes in such a way as to conse rve the energy of the whole system, and showed that this hypothesis leads t o surprising results.